Article 110—Requirements for Electrical Installations
Article 210—Branch Circuits
Article 430—Motors, Motor Circuits, and Controllers
Article 517—Health Care Facilities
Article 725—Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits
Article 800—Communications Circuits
Article 820—Community Antenna Television and Radio Distribution Systems
Grounding in patient care areas
Q: A redundant grounding system is required in some hospital areas. Section 517-13 requires an extra equipment-grounding conductor for electrical equipment in patient care areas. What are the dimensions of a patient care area in a patient bedroom? Is it necessary to require redundant grounding on all 125-volt, 15- and 20-ampere receptacles? If the answer is yes, how is this accomplished with a metal raceway wiring method?
A: Part of the definition for a patient care area reads like this: “Any portion of a health care facility wherein patients are intended to be examined or treated.” These areas are additionally classified as general care or critical care areas. Section 517-13(a) requires that all receptacles and noncurrent-carrying conductive surfaces of fixed electrical equipment likely to become energized, subject to personal contact, and operating at over 100 volts be grounded by an insulated copper conductor sized in accordance with Table 250-122 and installed in metal raceways.
Generally, all electrical equipment over 100 volts in a patient bedroom is covered by this rule, but there are exceptions. The first one allows metal cable wiring methods under restricted conditions in lieu of metal raceways. The second exception allows metal faceplates to be grounded by metal mounting screw(s) that secure the faceplate to a grounded outlet box or grounded wiring device.
The third exception eliminates the requirement for redundant grounding for lighting fixtures more than 7.5 feet above the floor, and switches that are more than 6 feet beyond the perimeter of the bed when in its nominal location. Switches that are more than 7.5 feet above the floor are also exempt from the redundant grounding requirement by the definition of patient vicinity in Section 517-3.
Four receptacles are required at each patient bed location. All receptacles installed must be listed “hospital grade.” This requirement applies to general care areas and is found in Section 517-18. At least six receptacles are required for each patient bed location in a critical care area.
The redundant grounding conductor must be connected to the equipment grounding conductor screw on the receptacle and the grounded metal box. Where the metal box is surface mounted, the bonding jumper between the receptacle terminal and outlet box is not required. If self-grounding hospital-grade receptacles are used with flush device boxes, the bonding jumper is not necessary.
Also, a bonding jumper is not required where isolated-ground receptacles are used. The rules for connecting the receptacle-grounding terminal to a box are in Section 250-146 and should be reviewed.
Overcurrent protection for motors
Q: We have a small job of installing two 5-horsepower, three-phase, 208-volt induction motors. The nameplate full-load current is 15.6 amperes. The owner wants to manually start and stop these motors using enclosed safety switches. Are there any NEC rules that will permit or prohibit this type of installation? If motor starters are not required, how do we size the motor overload protection and short-circuit and ground-fault protection?
A: Section 430-55 allows you to combine the overload protection, short-circuit, and ground-fault protection into a single overcurrent device.
Let’s do all the calculations for the motor branch circuit, overload protection, and short-circuit and ground-fault protection by starting with Section 430-6. This Section requires the use of the motor full-load current as given in Table 430-150 for sizing motor branch circuit conductors and the ampere rating of the disconnect switch. The full-load current shown on the motor nameplate is used to select the overload protection.
According to Section 430-22(a), the minimum conductor ampacity is 125 percent of Table value of full-load current. The Table full-load current for a 5-horsepower, 208-volt, three-phase motor is 16.7 amperes. Multiplying 16.7 by 1.25 results in a minimum conductor ampacity of 20.8 or 21 amperes. Table 310-16 lists the ampacity of a No. 12 copper conductor with 60 degrees Celsius or 75 degrees Celsius insulation as 25. Therefore, No. 12 copper conductors may be used for the motor branch circuits.
Motor disconnects must comply with Part J of Article 430. In particular, each disconnecting means must be readily accessible, plainly indicate whether in the “off” or “on” position, be a listed motor circuit switch rated in horsepower, and have a current rating that is at least 115 percent of the Table value of motor full-load current.
A three-pole, 30-ampere fusible safety switch with dual horsepower ratings should satisfy these requirements. Some motor circuit switches have two different horsepower ratings. For example: a three-pole, three-phase, 30-ampere, 240-volt safety switch could have a 3 horsepower rating with fast acting one-time fuses, and a 7.5 horsepower rating with dual-element time-delay fuses.
To provide overload, short-circuit, and ground-fault protection with one set of overcurrent devices, Section 430-44 requirements must be satisfied.
The Section reads: “Combined Overcurrent Protection. Motor branch-circuit short-circuit and ground-fault protection and motor overload protection shall be permitted to be combined in a single protective device where the rating or setting of the device provides the overload protection specified in Section 430-32.”
Assuming a motor service factor of 1.15, the overload protection is permitted to be 125 percent of motor nameplate full-load current. Doing the multiplication results in 19.5 amperes for the overload protection. However, Section 430-34 allows the rating of the overload protection device to be increased to a maximum of 140 percent of motor nameplate full-load current. Therefore, 20-ampere dual-element time-delay cartridge fuses may be used.
If the available fault current exceeds 10,000 amperes, Class R fuse kits should be installed to increase the limit to 100,000 amperes. Also, consideration should be given to providing heavy-duty safety switches to prolong installation life.
Some do not believe that substituting fuses for thermal overload relays provides adequate overload protection for the motor, because when an overload relay opens, all power conductors to the motor are deenergized, but when a fuse opens, two phases to the motor are still energized. These people generally fail to realize that when one fuse opens the rotor in the motor will stall, or if the motor continues to run, the current in the remaining two phases will increase and cause another fuse to blow.
The remaining fuse may or may not blow, but current flow to the motor will decrease or stop, thereby providing overload protection for the motor.
Low-voltage and power wiring in close proximity
Q: Does the National Electrical Code (NEC) permit Class 2, Class 3, telephone, and Cable TV conductors to occupy a hole in a wood stud that contains a nonmetallic sheathed cable operating at 120 volts?
A: According to the NEC, the answer is yes, but the communication cables may pick up interference from the nonmetallic sheathed cable.
In various places in the Code this construction is allowed as an exception. Section 725-54(a)(3) requires a two-inch separation of Class 2 and Class 3 wiring from electric light and power wiring, but Exception No. 1 removes the separation requirement where the electric light and power wiring, or the Class 2 or Class 3 wiring is installed in nonmetallic sheathed cable.
Communication cables are also permitted to occupy the same hole in a stud that contains nonmetallic sheathed cable. Section 800-52(a)(2) requirements are similar to those in Section 725-54(a)(3) but the language is different. A two-inch separation is required unless the electric power wiring is in nonmetallic sheathed cable, or other recognized wiring methods.
CATV coaxial cables are also allowed to share a bored hole in a wood stud with nonmetallic sheathed cable. An exception to Section 820-52(b)(2) permits this where the electric light and power wiring is in a raceway or in one of the cable assemblies mentioned in Exception No. 1.
Receptacle locations in hotel rooms
Q: During a recent stay in a hotel, the only place where I could plug in my computer was at receptacles behind furniture or under the bed. This hotel was built about six years ago. Should a receptacle be available without having to move furniture to comply with the NEC?
A: The 1999 NEC requires that at least two receptacles be readily accessible in hotel guestrooms, but this requirement did not appear in the 1993 and previous editions of the NEC. If the hotel was built six years ago, it was probably inspected under the requirements of the 1993 Code.
Section 210-60 required that the number of receptacles in guest rooms be determined by the requirements in Section 210-52(a), but the exception removed the spacing requirements by saying that receptacle outlets could be located convenient to the permanent furniture layout. Because of problems similar to the one described here, Code Making Panel No. 2 accepted proposals to require that at least some of the receptacles in a guestroom of a hotel or motel be readily accessible.
FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at (504) 254-2132.